WEDNESDAY, July 7 (HealthDay News) -- An immunochemical test
used to detect signs of colorectal cancer is less accurate when
done in the summer than in cooler times of the year, Italian
Although the particular brand of test used in the study -- the
OC-Hemodia test -- is not used in the United States, the findings
are of interest to U.S. researchers because immunochemical fecal
occult blood tests are gradually replacing the conventional stool
test for colorectal cancer, according to the report published in
the July 6 online edition of
Cancers of the colon or rectum generally have a good prognosis
when caught early, and the most common, non-invasive way to detect
it is a procedure known as the fecal occult blood test, or FOBT,
which looks for blood hidden in the stool.
In Italy -- unlike the United States -- the conventional
procedure is an immunochemical fecal occult blood test. In this
study, researchers noted that blood samples, if present, appeared
less stable at higher temperatures -- something that may have
implications for similar U.S.-based tests.
However, the study has important limitations in terms of the
U.S. population, one expert noted.
Dr. Durado Brooks, director of prostate and colorectal cancer at
the American Cancer Society, said that the Italian researchers
"looked at only one test, [and] there are a number these tests on
Moreover, the OC-Hemodia test is not approved by the U.S. Food
and Drug Administration and is thus not available in the United
States, he added.
Brooks also noted that most immunochemical fecal occult blood
tests used in the United States require several samples, as opposed
to the single sample of the OC-Hemodia test. Therefore, having
several samples tested may lessen the problem of inaccurate
results, if they exist, he said.
"So how relevant this is to other immunochemical fecal occult blood tests used in the U.S. is open to question," Brooks said. "But I think it's something investigators here might want to consider looking at and whether it is relevant to tests being used in the U.S."
In the United States, the conventional tool for non-invasive
colorectal cancer screening was traditionally the guaiac fecal
occult blood test, which involves testing stool smears for hidden
blood. However, since 2004, the U.S. Food and Drug Administration
has approved many immunochemical fecal blood tests for marketing.
Many U.S. health systems, in fact, consider a series of the
immunochemical screens best practice.
This is partly because conventional FOBTs require complex
dietary restrictions that make it hard for some patients to comply.
Patients are not supposed to eat meat, cantaloupe, vitamin C,
anti-inflammatory drugs, citrus fruits and various other foods and
supplements for three days before the test, and false positives can
result if the patient inadvertently consumes certain foods,
vitamins or drugs in the days before the test.
For the Italian study, lead researcher Dr. Grazia Grazzini, from
the screening unit at the Cancer Prevention and Research Institute
in Florence, and colleagues looked at the effect of temperature on
the accuracy of fecal occult blood tests among individuals in the
Italian national screening program in Florence over several
The investigators included temperature variations between
sampling and the return of the test sample, which took about a
week. They also accounted for the amount of time that the samples
were in the laboratory refrigerator, which was about four days.
In all, they looked at 199,654 tests. Each sample was tested for
hemoglobin (Hb) levels, which is the protein in blood that colors
Grazzini's team found that hemoglobin levels were significantly
lower in the summer months. Hb levels averaged 27.6 nanograms per
milliliter (ng/mL) in spring, 25.2 ng/mL in summer, 29.2 ng/mL in
autumn and 29.5 ng/mL in winter.
Accordingly, tests done in summer had a 17 percent lower
probability of testing positive for signs of colon cancer compared
with tests done in winter. In fact, every one degree Celsius
increase in temperature reduced the probability of a positive
result by 0.7 percent, the researchers found.
In all, tests done in summer were 13 percent less likely to pick
up signs of cancer than tests done in winter, Grazzini's group
found. "During the summer, significant [cancerous changes] will be
missed," the authors warned, noting that this could have serious
implications for the risk of interval cancers, which are cancers
that develop between screenings.
"This is the first study that investigated about stability of immunochemical fecal occult blood tests related to ambient temperature. These results will have important implications for the organization of immunochemical fecal occult blood test-based screening programs, particularly in countries with high ambient temperatures," Grazzini stated.
"It is important to consider stability of immunochemical fecal occult blood tests for the quality assurance of the colorectal screening program," Grazzini added. "Immunochemical fecal occult blood tests showed in the past very good performance for early diagnosis of colorectal cancer. For this reason, our results will allow for improving stability of fecal samples and therefore quality of [the] screening program."
Among other things, the researchers recommended refrigerating
samples directly after testing and during transportation to a
For more information on colorectal cancer, visit the
American Cancer Society.